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Tony Leggett

by Michael Nielsen on January 28, 2005

At today’s physics colloquium, Tony Leggett gave a rather striking talk about tests of quantum mechanics. It was striking because, if I understood him correctly, about five years ago he thought it likely that quantum mechanics (specifically, the superposition principle) would break down at macroscopic levels. It’s a very interesting, uncommon, and refreshing point of view.

Apparently, he’s much less certain of this now, in part because of the experiments done over the past few years with superconducting qubits. He still regards Bell inequality violations in such systems as important, however.

From → General

4 Comments
  1. It’s funny. I always expect that quantum theory will fail in the opposite direction: it will fail for the very small. Mostly this is probably because I buy most of the arguments about the emergence of the classicality from the quantum world.

    And really, isn’t it true that it is at the very small scale that we don’t understand what is going on? Take for example quantum field theories, which most believe are low energy approximations to something deeper theory (which may or may not be a field theory). High energy equals short wavelengths, so really what we know now is that our theories are good all the way down to the very small. When we extrapolate to the infinitely small we get serious difficulties. So if quantum theory fails somewhere, I’m betting it fails at small distances.

  2. Michael Nielsen permalink

    Leggett seems to base his thinking on the idea that macroscopic superpositions will NEVER be allowed, which is why he’s so interested in superconducting qubits, and Bell inequality violations.

    It’s certainly a regime that hasn’t been probed at all until very recently, much as the very high energy / small length scale regime hasn’t been probed, and that’s certainly the sort of place to be looking for violations.

  3. mitch p. permalink

    I don’t suppose he talked about this very recent article, claiming detectable quantization of a collective vibrational mode in a nanostructure of 50 billion silicon atoms?
    http://nano.bu.edu/quantized-motion.pdf

  4. Michael Nielsen permalink

    If he did, I missed it. It couldn’t have been more than in passing, as I think I followed most of the talk pretty well.

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